Uranium Extraction from Seawater

Ken Ferguson
March 21, 2012

Uranium in Seawater

Many people do not realize that seawater has a
natural concentration of uranium. The percentage of uranium in seawater
is quite low, as one may expect. It has been shown that the uranium
concentration of seawater is only about 3 parts per billion, which is
about 3 milligrams of uranium per cubic meter. [1] The total volume of
the oceans is about 1.37 billion cubic kilometers, so there is a total
of about 4.5 billion tons of uranium in seawater. Assuming we could
recover half of this resource, this much uranium could support 6,500
years of nuclear capacity. [2]

Extraction Methods

Shortly after World War II, recovery of seawater by
ion-exchange resins was being considered. [3] It was deemed more
economically viable to focus on exploitation of known uranium ores,
though. It was later determined that an economically acceptable method
of uranium extraction from seawater may be found, which has prompted
more research in the area.

To extract uranium from seawater, people are using
organic and inorganic absorbents. [3] For extraction to be successful,
the extractant must work efficiently at the normal pH level and ionic
strength of seawater. The extractant must also be nearly insoluble. [3]

A group from Japan Atomic Energy Research Institute
designed a fabric absorbent to extract uranium from seawater in 2002.
[1] They prepared a polymeric absorbent in a nonwoven fabric, which
contained an amidoxime group that was capable of forming a complex with
uranyl tricarbonate ions, which is the type of group required to yield a
maximum absorption rate of uranium. [1] They then submerged an
absorption cage that had a 16 square meter cross-sectional area cage
that was 16 centimeters in height into the Pacific Ocean. The cage had
144 stacks of the nonwoven fabric, with each stack consisting of 120
sheets of the fabric.
Over the next two years, a total of 450 submersion days, the group
extracted 1083 grams of uranium, with an average absorption rate of
0.00133 grams per day per stack. [1]

Economic Viability

Is seawater extraction economically viable? Japanese
research suggests the lowest possible cost to extract uranium is 25,000
Yen per kilogram of uranium. [4] At the current exchange rate (March
2012, 1USD ~ 81 JPY), that equates to about 300 USD per kilogram of
uranium. This is about 3 times more than the current price of uranium,
and it is expected that the actual recovery price would be about 10
times the current price of uranium. [2]

Conclusion

Seawater naturally has a concentration of about 3
milligrams of uranium per cubic meter, and some people have become very
excited about the vast amount of uranium in the ocean. Methods of
extracting this uranium has mostly been worked on by the Japanese, who
have come up with a method of extraction which would cost about 300 USD
per kilogram of uranium. This is about 3 times the current price of
uranium, but we may one day need this uranium to solve the worlds energy
needs.

The extraction of uranium from sea water has been
discussed in a previous PH241 report. [5]